Approximately 40,000 women in the U.S. die annually from breast cancer. Furthermore, the relapse rate is estimated at 15% of 210,000 diagnosed cases per year. This comprises a patient population of about 72,000, who at present do not have effective therapies available to them. Because most current anti-cancer drugs suppress the growth of cells, the targeting of cancer metastasis is innovative and has the potential to serve a large patient population, which has poor prospects for survival. The cytokine osteopontin is produced in abundance by breast cancer cells, and it is known to be important in metastasis. However, the full-length form, osteopontin-a, is also critical for cellular immunity and may have pro-adhesive properties. Breast cancer cells express multiple splice variants of osteopontin. The shortest form, osteopontin-C, enhances anchorage independent growth [He et al. 2006. Oncogene 25:2192]. Osteopontin-C is present in about 75% of cancers, but is absent from normal breast tissues. [Mirza et al. 2007. Int J Cancer. In press, e-pub. ahead of print]. We have developed monoclonal antibodies to osteopontin-C that have neutralizing activity in soft agar. Here we propose to further study the properties of these antibodies, in vitro and in vivo, to evaluate their potential as therapeutic agents. This is significant because the inhibition of a functionally important molecule that is present on about 3 of all breast cancers will provide the majority of patients who currently succumb with treatment options. Specific Aim 1: Screen anti-osteopontin-C antibodies for neutralizing activity in cellular assays (soft agar growth, anoikis). Specific Aim 2: Screen anti-osteopontin-C antibodies for neutralizing activity in molecular assays (luciferase reporter, Biacore). Specific Aim 3: Test the anti-cancer activity of anti-osteopontin-C antibodies in a xenograft model of human breast cancer metastasis (longitudinal monitoring with IVIS imaging). The proposed validation of the anti-osteopontin-C monoclonal antibodies is a critical early step in the path to humanization, toxicity studies, FDA approval as innovative new drug, and clinical trials. Upon completion of the experiments proposed here, the initiation of clinical trials can realistically be reached within two years. PUBLIC HEALTH RELEVANCE:Most cancer patients die from the spread of the tumor cells throughout the body (metastasis). However, most treatments inhibit only the growth of tumors. We have identified a molecule that is selectively present in breast cancer cells, but not in healthy breasts, and is important for the spread of breast cancer to other organs. MetaMol Theranostics has made an antibody to this molecule, which can supplement existing cancer therapies by suppressing metastasis. [unreadable] [unreadable] [unreadable]